Automatic transmissions are increasingly being used in motor vehicles to relieve the driver from gear-shift operations, particularly in large-city traffic, which could distract his/her attention from traffic events. Newer-generation automatic transmissions are safer and easier to operate. The transmission control of automatic transmissions may be influenced with respect to the driving modes “sport” or “comfort” via a selection to be made on the part of the driver at an operating switch or a push-button switch.
German Patent Application No. DE 199 63 782 relates to a control for a vehicle having a transmission control. A plurality of electrical switching elements, such as a kickdown switch, a brake-lights switch or a selector-lever position switch exchange signals with a transmission control. The same holds true for other switching elements such as a manual-mode switch, an upshift transducing sensor or a downshift transducing sensor, as well as for a program-selector switch (economy/sport switch). The associated signal lines are run to a control unit that is connected to a serial bus system (CAN). The combined, transmitted signals are conducted via the CAN data bus to the transmission control.
German Patent No. DE 44 41 896 relates to the control for a motor vehicle having an automatic transmission. The transmission control of the motor vehicle is connected by signal lines to a selector lever, a kickdown switch and a driving-program selector switch. The driver of the motor vehicle inputs his/her commands or wishes into the transmission control via these interfaces. Driving positions P, R, N, S, 1 and 2 are selected via the selector lever, the demand for a sharp acceleration is made via the kickdown switch, and the choice between an “economy” and a “sport” driving program is made via the driving-program selector switch.
In the Automobiltechnische Zeitschrift (Automotive Engineering Magazine) volume 95, year 1993, p. 420 ff. in “Die adaptive Getriebesteuerung für BMW-Automobile” (Adaptive Transmission Control for BMW Automobiles), an adaptive transmission control (ATC) is described by which the ratio of transmission may be adapted to the behavior of the driver and the environmental conditions prevailing in each instance. Moreover, the adaptive transmission control ATC evaluates a plurality of further parameters. In this context, the accelerator has the greatest influence on the gear selection. Thus, given a quick let-up on the accelerator, upshifts are prevented, and downshifts are triggered (kickdown) in response to complete depression of the accelerator. In addition to these well-known functions, the ATC includes a multitude of less striking features which contribute to an intelligent gear selection in widely varying driving situations. Besides the gear selection, the transmission control controls the sequences of gear shifts, executes diverse safety functions and documents possibly occurring errors for the subsequent diagnostic. The multitude of complex tasks requires the use of highly developed hardware and extensive software. Until now, the gear selection of automatic transmissions was made taking into consideration the throttle angle, the speed at the transmission output, the position of the kickdown switch and selector-lever switch, as well as the actuation of the program-selector pushbutton. Only a little new information was made available to the control unit to enable consideration of the additional aspects which the ATC utilizes for optimizing the gear selection. One innovation is the processing of the four-wheel speed information supplied via the ABS control unit. The longitudinal acceleration and lateral acceleration of the vehicle, as well as the slippage of the driven wheels may be derived from these values. Moreover, the brake-lights switch is queried in order to detect the actuation of the brake pedal. In automobiles equipped with an automatic stability control (ASC), the pushbutton by which the driver is able to deactivate this system is also queried. To derive the suitable transmission ratio from the diverse input information, two tasks, namely, the shift-program selection and the gear selection are executed in the transmission control. First of all, a shift program must be stipulated. When working with conventional transmission controls, this is accomplished in that the driver, using the program-selection pushbutton, selects, for example, economy program, sport program and winter program from an easily comprehensible offering of programs. Given a selection of nine shift programs, however, this would place too great a demand on the driver, so that there should be software support. To that end, functions have been introduced within the framework of the adaptive transmission control ATC which evaluate the behavior of the driver based on his/her measurable actions. The position and the movement of the accelerator, the instantaneous traveling speed, the actuation of the kickdown switch and the occurrence of lateral accelerations are analyzed. The linkage of this information supplies a “driver-type characteristic”, resulting in the call-up of one of four basic programs. Under special environmental conditions, special programs are used. Thus, on a slippery roadway, a winter shift program is used to increase traction and directional stability. When driving on uphill stretches or under unusual load, programs oriented toward vehicle performance are used which are able to help in reducing the frequency of shifting under these conditions.
The gear selection is subsequently made, taking the ascertained program as a basis. To that end, by way of upshift and downshift characteristic curves, a connection is produced between the measured values for traveling speed and throttle angle, respectively, at the gear changes. The shifting characteristics are basically obtained in such a way that upshifts are initiated by let-up of the accelerator or increasing velocity—downshifts by depression of the accelerator or reduction of the velocity. The fixed relation between the shifting characteristic and the gear selection is canceled by several functions of the adaptive transmission control ATC. Thus, upshifts which would take place according to characteristic curves may be prevented, or downshifts may be triggered even when no downshift characteristic was exceeded.